1. Field of the Invention
The present invention relates to a self-diagnosis circuit that diagnoses for an abnormality in a high-frequency circuit.
Priority is claimed on Japanese Patent Application No. 2012-102591, filed Apr. 27, 2012, the content of which is incorporated herein by reference.
2. Description of the Related Art
Wireless communication apparatuses have been commonly used in recent years in various fields because the wireless communication apparatuses have the advantages of not requiring the laying of communication lines, and can be easily installed in locations in which the laying of communication lines is difficult or the laying construction is uneconomical. For example, in plants and factories, on-site equipment (measuring instruments and actuators) capable of wireless communication and referred to as wireless field devices are used as the above-noted wireless communication apparatuses, with measurement signals indicating measurement results from wireless field devices and control signals for controlling the operation of wireless field devices being transmitted and received by wireless communication.
When an abnormality such as misoperation or a failure occurs in such a wireless communication apparatus, in order to facilitate quick notification of the occurrence of the abnormality and identification of the cause thereof, a self-diagnosis circuit is provided to diagnosis for the existence an abnormality in the high-frequency circuit provided therewithin. This self-diagnosis circuit is provided, for example, in the transmitting circuit that transmits wireless signals, or in the transmitting and receiving circuit that transmit and receive wireless signals, and splits off a part of a high-frequency signal that propagates along the signal transmission path toward the antenna, and diagnoses for an abnormality, in accordance with the magnitude of the signal level of the split-off high-frequency signal.
Japanese Laid-open Patent Publication No. 2000-36767 discloses an example of a self-diagnosis circuit that diagnoses whether or not the high-frequency circuitry (pre-amplifier, power amplifier, and attenuator) of a transmitter is normal. Specifically, in Japanese Laid-open Patent Publication No. 2000-36767, self-diagnosis is done before transmission to detect the amplitude value of the various outputs of the high-frequency circuitry, and by comparing the various output amplitude values with normal amplitude values, a judgment is made as to whether or not the various circuits of the high-frequency circuitry are normal.
A conventional self-diagnosis circuit, as described above, basically diagnoses for an abnormality in accordance with the magnitude of the signal level of a high-frequency signal that propagates along the signal transmission path toward the antenna. For this reason, although it is possible to detect an abnormality in the previous stage included in the high-frequency circuit provided in a wireless communication apparatus, it is difficult to detect an abnormality in the follower stage. In this case the previous stage included in the high-frequency circuit refers to the circuitry from the input part to which the high-frequency signal is input up to the part in which the self-diagnosis circuit is provided, and the follower stage included in the high-frequency circuit refers to the circuitry from the part in which the self-diagnosis circuit is provided up until the output part from which the high-frequency signal is output (or up to the antenna).
Conventional wireless communication apparatuses often have an LCD (liquid-crystal display) to display the diagnosis result of the self-diagnosis circuit on the LCD, and to give notification that an abnormality has occurred. However, wireless communication apparatuses are often installed in locations at a distance from the communication destination to which the communication is intended, and when a wireless communication apparatus is installed in an out-of-the way outdoor location, it is difficult to quickly discover that an abnormality has occurred. In particular, in the above-described wireless field devices, because there are times when they are installed at distances as much as several hundred meters to several kilometers, unless patrols are frequently made to visit the wireless field devices, it is not possible to know of the occurrence of an abnormality.
Some aspects of the present invention are to provide a self-diagnosis circuit for diagnosing for abnormalities, not only in the previous stage, but also in the follower stage included in a high-frequency circuit, and for facilitating knowledge of the occurrence of the abnormality.